The perfect way to travel is at a constant speed (ideally around 50mph), and in the highest gear (five or six). So if you're a patient driver, you'll have lower fuel bills - it's as simple as that. It's unrealistic to avoid overtaking, but there's little point accelerating past a car to simply be in front of it at the next set of lights - any instant gratification will appear on your fuel bill the next time you fill up.